<html>
    <head>
        <title>Test</title>
        <style>

meter.custom {
  appearance:none;
  background-color:gold;
  color:red;
}

        </style>
        <script></script>
    </head>
    <body>
      <p>default styling: <meter value="0.5" /></p>
      <p>custom styling: <meter.custom value="0.5" /></p>
    </body>
</html>